Atmospheric scientists trace the human role in Indonesian forest fires
Published: Sunday, February 22, 2009 - 15:29 in Earth & Climate
Learn more about: air quality conditions atmospheric scientists greenhouse gas 
emissions indonesian forest fires
Related images
(click to enlarge)
Fire and smoke from a burning peat forest on Pedang Island in Riau Province, 
Sumatra, Indonesia. The island is covered by forested peat up to 15 meters in 
depth. The excessive smoke is a common feature once the fire consumes the 
above-ground material and burns into the peat, which remains moist, but just 
dry enough to smolder. The photo was taken in July 1991 during the El 
Nino-induced dry season. The forest was slashed before burning. Intact forest 
on peat rarely burns. Riau province currently has the highest rate of 
deforestation in Indonesia.
Photo by Michael Brady, Canadian Forest Service.

Severe fires in Indonesia – responsible for some of the worst air quality 
conditions worldwide – are linked not only to drought, but also to changes in 
land use and population density, according to a new study in Nature Geoscience 
led by Robert Field of the University of Toronto. "During the late 1970s, 
Indonesian Borneo changed from being highly fire-resistant to highly fire-prone 
during drought years, marking the period when one of the world's great tropical 
forests became one of the world's largest sources of pollution," says Field, a 
PhD student of atmospheric physics. "Ultimately, this abrupt transition can be 
attributed to rapid increases in deforestation and population growth. The 
resulting occurrences of haze currently rank among the world's worst air 
pollution episodes, and are a singularly large source of greenhouse gas 

Sumatra has suffered from large fires at least since the 1960s, but Indonesian 
Borneo seems to have been resistant to large fires – even in dry years – until 
population density and deforestation increased substantially and land use 
changed from small-scale subsistence agriculture to large-scale industrial 
agriculture and agro-forestry.

"We've had a good understanding of fire events since the mid 1990s, but little 
before this due to the absence of fire data from satellites," says Field, who 
collaborated with Guido van der Werf of VU University Amsterdam and Sam Shen of 
San Diego State University. "However, one of the major impacts of large-scale 
fires is a reduction in visibility due to the smoke produced. Visibility is 
recorded several times a day at airports in the region, and these records 
proved to be an excellent indicator of severe fire activity. We were able to 
piece together visibility observations back to the 1960s, and hence develop a 
longer term record of the fires."

Having a long-term record of the fires allowed the scientists to better 
understand their causes. "Using weather records, we were able to estimate the 
specific rainfall level below which large fires have occurred in the previous 
two decades. In turn, we found that the rainfall over Indonesia was influenced 
equally by the Indian Ocean Dipole and the El Niño Southern Oscillation 
phenomena. Hopefully, this information can be used to better anticipate and 
prevent future haze disasters in Indonesia."

Field says that there is a direct link between the increased prevalence of 
severe fires and haze disasters and the man-made change in land use. "The 
visibility record also showed, quite strikingly, the impact of human settlement 
on a previously pristine tropical forest. This should give pause to further 
agro-forestry expansion in Indonesia, particularly for oil palm as a source of 

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